Algorithms And Key Techniques Of Digital Watermarking Of 3D Models

The rapid development of computer and Internet related technologies makes not only accessing digital media products much convenient, but also raising issues, such as copying randomly, unauthorized usage and modification. There is the same problem of copyright protection for 3D models. Especially, with the research and development of collaborative design and virtual products on network environment, copyright protection of 3D models is becoming increasingly important. In this dissertation, some 3D model watermarking techniques are studied. The main contributions of this dissertation are:Watermarking scheme for 3D point model based on geometry property distribution: Watermark is embedded by modifing the mean value of vertex distance; Hausdorff is measured for the deformation between the original model and the watermarked model. Through statistical analysis, getting experimental results of the strength coefficientζand the length coefficient L of the watermark, we set the different value of L andζ, so that there is a good balance between the coefficients and geometric error. Mesh pre-processing is not required before watermarking is embedded into the point model in the algorithm. Experiments show that this scheme is fairly robust against attacks, such as affine transformation, resorting, simplification, cropping, nosing and various distortion ones with local geometric alterations.3D mesh watermark based on feature informations: Feature patches of mesh models are obtained by watershed segmentation, and then a string is transformed into watermark matrix by image watermark based on Fast Fourier Transform. At last, watermark inatrix is added into vertex coordinations. Experiments show that this algorithm is robust against cropping, rotation, translation, scaling and resorting.Two multi-watermarking methods for 3D meshes: The first watermarking algorithm is to choose appropriate vertexes according to 1-ring of each vertex, and build their own local coordinate system. The first string watermarking is embedded by adjusting coordinate of these vertexes. The second image watermarking is embedded using redundancy information of triangular shape. Watermarks are embedded into two different parts of mesh. One is coordinate of the vertex; the other is sequence of connections of the vertexes of each triangle. The two carriers will not be disturbed each other. Therefore, it ensures that watermarks signal will not be affected each other during embedding process and extracting process. Experimental results show that the algorithm is robust to some attacks, such as affine transformation, un-scaling, noise addition, cutting, and vertex reordering. The second watermarking algorithm is to improve 3D mesh watermark based on mesh segmentation and image watermark. In order to resist against more attacks, such as noising, unscaling etc, image watermarking is embedded into topology information of mesh model. Experiments show that double watermarking shceme is an effective way to improve the robustness of watermark.Watermark of subdivision surfaces based on DCT: The original mesh is subdivided three times. A distance matrix is built according to the ascending order based on vertex's distance. Then DCT transform is carried out. In order to improve the transparence of watermark, watermark information is prepocessed by a Fast Fourier Transform watermarking algorithm; at last a watermarking matrix is obtained. A watermark mesh is obtained by adding watermark matrix into distance matrix. Experimental resut shows that this algorithm is robust against translation, rotation, cropping noising and some combination attacks.